I was traveling on a horse and I went in the water. I fell off the horse and I couldn't swim. I press X button on the PS4-controller but I couldn't swim. I sinck to the bottem of the river and I drowned. 

After that I start again and I walk back to the location where I drowend. I collect all my items and my horse. They were still there. Then I try again and ride on the horse again and I went into the water; and it happen again; I fell from the horse and I drowend again.

Than I start again, I went back to the location where I drowend. I collect all my items and my horse again, and then I travel on the horse back to my start location (x=0 z=0). I try several time to went into the water with the horse, but I didn't happen again. I fell of the horse and I could swim. Then I thought it only happen on a specific location in the game. I start to travel again in another direction, but when I jump with the horse into the first sea I fell off the horse and I drowned again.

Can someone take a look at this issue? Thank you.